1. Field
The present invention relates to a medical handpiece, including a surgical handpiece, for driving a medical tool.
2. Description of Prior Art
Such medical or surgical handpieces serve to drive medical tools, e.g., saws, drills or surgical drill wires. To do so, the tools are attached to the handpiece by coupling devices. A plurality of different tools can therefore be operated by using one handpiece.
Surgical drill wires are used for treating fractures in surgery. In this procedure, the drill wires are rotated, preferably by a driven handpiece, and drilled into the bone material. By repeating the sequence “drilling into the bone material, releasing the chucking device, resetting the handpiece, renewed chucking of the wire and drilling” several times, the drill wire can be introduced into the bone material easily by using the handpiece and without applying much force.
To be able to design the length of these surgical drill wires independently of the driven handpieces, in particular the chucking devices holding the wire, the handpieces provided for this application are provided with through-bores for the wire, extending through the interior of the handpiece. Drill wires of any length may thus be accommodated in the chucking device and driven by means of a drive, preferably to rotate or to oscillate.
U.S. Pat. No. 5,207,697 describes such a medical or surgical handpiece for holding a surgical drill wire in the interior of the handpiece, in particular in its drive train.
This known surgical handpiece for introducing drill wires into bone material has a handpiece housing with an electric drive accommodated therein, having a first drive shaft and a first drive rotational speed. This first shaft is connected by a gear to a second output shaft arranged coaxially with the first shaft. This shaft, rotating at a second, lower output rotational speed, serves to drive a coupling device for a surgical tool that can be attached to the handpiece, in particular for a surgical drill wire. A second housing opening coaxial with the two shafts of the drive train for insertion of a wire through the shaft configuration to accommodate the wire in the coupling device is provided on the opposite side of the receptacle opening for the coupling device. Because of the different rotational speeds of the multiple shafts of the drive train, there has been abrasion in the past, leading to breakage of the drill wire. To avoid this abrasion of the drill wire, the output shaft according to the present document is lengthened by means of a third shaft extending through the drive shaft. This ensures that only one output rotational speed, namely that of the second and third shafts, which are joined together, acts on the drill wire through the entire handpiece.
One disadvantage of this design of the handpiece for driving a medical tool, in particular a surgical drill wire, has proven to be the dependence of the rotational speed acting on the wire on the shaft configuration of the drive train. The rotational speed of the shaft configuration guiding the drill wire through the handpiece, namely the interconnected second and third shafts, is determined by the motor in the handpiece and its gear. If different tools are connected to the handpiece, as indicated above, this necessitates different drive rotational speeds. The respective coupling devices belonging to the tools therefore have additional gear configurations to adapt the output rotational speed of the handpiece to the predetermined drive rotational speed of the tools. Consequently, there is another rotational speed difference that is not taken into account in the prior art, namely the difference between the output rotational speed of the handpiece and the drive rotational speed of the coupling device. This again results in damage to the drill wire.
Another disadvantage of the embodiment known in the prior art is the lack of bearing support of the third shaft. Due to the arrangement of the third and/or lengthened second shaft in the drive shaft without additional bearing support with respect to the drive shaft, the result is merely a displacement from abrasion on the drill wire to abrasion on the third shaft. By inserting the drill wire through the shaft configuration, in particular through the third shaft, into the coupling device and resetting the handpiece in drilling the wire into the bone material and also because of the inherent imbalance of the wire in the driven state, contact between the first and third shafts which are arranged one inside the other and driven at two different rotational speeds is unavoidable without separate bearing of the third shaft. This ultimately leads to increased wear on the third shaft.